統計機率的問題(英文的)

Question

Q:

three boxes identical in appearance contail the following coins:
box X - 2 quarters,
box Y - 1 quarters, 2 dimes
box Z - 1 quarters, 1 dimes
if a coin drawn at random from a box selected at random is a quarter,
what is the probability that the randomly selected box contains at least one dime?

答案為:5/11
(我有詳細解答,可是我看不懂,如果要看可以說ㄧ聲,不過我會直接用相機拍,因為電腦打字太麻煩了)




*要把題目的中文翻譯打出來,因為我完全看不懂!!!

*雖然我有詳解,可是我看不懂,所以你寫的答案最好不要太過"深奧"
就~每ㄧ個步驟都要清楚明瞭

*if a coin drawn at random from a box selected at random is a quarter,
這裡的"a quarter"是代表什麼意思??是機率1/4還是25分錢??

Answer 1

three boxes identical in appearance contail the following coins:
box X - 2 quarters,
box Y - 1 quarters, 2 dimes
box Z - 1 quarters, 1 dimes
if a coin drawn at random from a box selected at random is a quarter,
what is the probability that the randomly selected box contains at least one dime?
3個相同的盒子各含(contain,不是contail)2個1/4元(quater),1個quater+2個1角, 1個quater+1角
由這些盒子中任取出一個銅板(coin),若此銅板為1/4元,問該盒中至少1個dime的機率=?
解法:
任取一盒機率各為1/3,
再取得1個quater=>3種case:
(1)x盒: p1=1/3*1
(2)y盒: p2=1/3*1/3
(3)z盒: p3=1/3*1/2
=>取得1個quater之p=p1+p2+p3=11/18, 該盒至少1個dime之p=p2+p3
Ans:(條件機率) p=(p2+p3)/(p1+p2+p3)=5/11